The present invention relates to luminescence systems and methods, and more particularly relates to instruments and methods for the chemical analysis of substances by the measurement of fluorescence and phosphorescence emission properties.
The chemical analysis of luminescent substances with instruments that employ light to excite samples of such substances and measure light emissions therefrom has become an essential tool in a variety of fields. For example, in the fields of health care, environmental science and industrial process control, to name a few, fluorometric chemical analysis of luminescent substances is being employed primarily because of its sensitivity and selectivity.
In general, luminescence analysis involves a process in which a sample, exposed to radiation of one wavelength, absorbs this radiation and reemits radiation of the same or a longer wavelength.
Luminescence is the emission of visible or invisible radiation unaccompanied by high temperature by any substance as a result of absorbtion of exciting energy in the form of photons. It is a general term which includes both fluorescence and phosphorescence. A fluorescence lifetime is the characteristic time it takes for a fraction of the excitation energy contained in a molecule to be re-emitted as light. The characteristic fraction is 1/e of the initial excitation intensity. In the present invention, if this re-emission occurs after about 10.sup.-8 seconds, it is called fluorescence. Reemission after about 10.sup.-6 seconds or more is called phosphorescence. The re-emissions are used to determine the material which is the source of the fluorescence or phosphorescence. This basic process has virtually become an essential analytical tool in many fields because of the superb sensitivity that it offers over other systems. For example, with spectrophotometers, detecting micromolar concentrations is a major task. With luminescence type measurements, detecting picomolar concentrations is routine. Luminescence measurements can reveal much more than just concentration They can detect structural changes and orientation as well by means of lifetime measurements and other related measurements.
Determining the fluorescence lifetime of a compound is the most exacting of the measurements of fluorescence properties. This is primarily due to the forementioned extremely brief time period of the emission, typically 10.sup.-12 to 10.sup.-8 seconds. Of necessity therefore, prior instruments for determining fluorescence lifetimes have been complex, expensive and difficult to use.
Although such systems have been used successfully, they have generally been accepted as a routine tool in only the most sophisticated installations primarily because of cost, structural and operational complexity, and difficulty in interpreting results. Attempts to produce systems that are relatively simple and less expensive have often resulted in systems of greatly reduced precision. As such, those concerned with the development of systems that measure fluorescence and phosphorescence emission lifetime properties have recognized the need for a simple, inexpensive automated system that maintains at least the same high precision of prior art systems. The present invention fulfills this need